Activation of cellulose for acylation



Patented Aug. 9, 1949 ACTIVATION F CELLULOSE FOR ACYLATION William B;Hincke, Kingsport, Tenn., and Carl J. Malm, Rochester, N. Y., assignorsto Eastman Kodak Company, Rochester, N. Y., a corporation of New JerseyNo Drawing. Application June 27, 1945, Serial No. 601,918

Claims. (Cl. 260225) This invention relates to the activation ofcellulose preparatory to acylation in which the cellulose in the form ofa slurry in distilled or demineralized water free of added chemicals isboiled 2-4 hours and the water is removed by means of lower fatty acid.

Cellulose, particularly wood pulp cellulose, as

normally obtained, even that classifiable as re-" fined high a cellulosematerial, contains a small amount of hornified amorphous material whichis particularly resistant to acylation. Even though the cellulose ismechanically disintegrated or opened up to assure contacting of theacylating liquids with all the particles of cellulose it is stilldifficult to uniformly acylate cellulose containing hornified materialwith fatty acid anhydride and catalyst. Often a residual haze is foundin the reaction mass resulting after acylation which can be removed onlywith great difficulty.

To facilitate the acylation of cellulose pretreatment with acetic acidhas been resorted to. Glacial acetic acid, as normally employed inpretreatment operations, leaves much to be desired as a swelling agentfor the horny material found in some cellulose, and the anhydrous fattyacids having more carbon atoms than acetic, such as propionic orbutyric, are of much less value than acetic acid for facilitating theacylation reaction with fatty acid anhydride. The use of higher thannormal amounts of catalyst, higher temperatures or longer times ofreaction in the subsequent esterification step do not compensate for thepoor pretreatment and result in more complete acylation of the cellulosebut only in more 4 breakdown or acetolysis of the cellulose in the finalcellulose ester. Such intensified operations result in a cellulose esterhaving a viscosity too low for use in preparing commercial products.

One object of our invention is to provide a method of activatingcellulose, particularly that having some horny, unreactive particlestherein, to render it readily and uniformly reactive with lower fattyacid anhydride in ordinary cellulose acylation processes. Another objectof our invention is to provide an effective method of activatingcellulose requiring but a short time of treatment. A further object ofour invention is to provide a method of activating cellulose, in whichwater acts as the activating agent yet the pretreated cellulose isobtained in the form of cellulose mixed with only a small proportion oflower fatty acid. Other objects of our invention will appear herein.

by forming the cellulose into a slurry in low mineral content water,without the addition of chemicals thereto, boiling the slurry for 2 to 4hours and then removing the water from the cellulose with lower fattyacid so that there results an activated cellulose moistened with thelower fatty acid. 1

Our pretreatment method may be applied to any cellulose, suitable foracylation purposes, which can be slurried with water, an advantage beingthat only a short time of treatment is necessary. Our pretreatmentmethod however is particularly adapted to cellulose which has anonuniform nature -because of the presence of horny, amorphous particlesdistributed therethrough. For instance, acetylation grade wood pulpcellulose is supplied ordinarily in the form of rolls of dry sheets'inwhich hard particles of cellulose are found distributed through thesheet.

The cellulose in accordance with our invention is mixed with or agitatedin 15 to 25 parts of distilled or low mineral content water (per part ofcellulose) to form a suspension or slurry of the cellulose fiberstherein. The water used is one which has a mineral content of less than20 parts per million. I This may be distilled water or a demineralizedwater. Obviously the lower the mineral content, the more suitable is thewater for use in our activation process. The term .low mineral contentwater as used herein is to be understood as referring to water having amineral content of 0-20 parts per million therein. The proportion ofwater employed is not critical being suificient togive a good slurry andconducive to uniform boiling. At least 15 parts of Water is ordinarilynecessary for this. The cellulose after suspending in water is subjectedto boilingforfrom z to 4 hours and a highly activated cellulose results.

Before using this cellulose for esterification it is desirable to,remove the water therefrom. It is a feature of our invention that thewater is removed from the cellulose in such a manner that the productconsists of highly reactive cellulose moistened bylower fatty acid. Thewater may be directly removed from the cellulose with fatty acid,howevenremoval is best and most economically accomplished by firstremovin the bulk of the water from the cellulose by mechanical meanssuch as by means of squeeze rolls, screw presses, suction filters,centrifuges or the like. To retain the swollen reactive condition of thecellulose the'remaining 1-2 parts of water present therein is extractedor displaced with a These objects of our invention are accomplishedlower fatty acid, either acetic, propionic or butyric tained is suitablefor charging directly to the I acylation mixer for direct acylation withfatty acid anhydride and catalyst.

The activated cellulose obtained may be employed for making celluloseacetate or cellulose mixed esters in which acetic anhydride is employedas the esterifying agent or for makin high propionyl or high butyrylcellulose esters. In making the latter at least a large proportion oreven the entire anhydride may :be propionic or butyric anhydride as theesterifying agent. As these anhydrides are more sluggish in acylat ingeffect than acetic anhydride, it is important that the celluloseemployed therein be highly reactive. Although ordinarily acetic acidwill be employed to displace the water on the cellulose, in .these caseswhere little or no acetyl is desired in :the cellulose esterificationmixture, butyric .or propionic acid may be employed for this purpose.

tion:

Example I "One part of wood cellulose sulfite pulp, having a high(it-cellulose content was slurried with parts or demineralized waterhaving a mineral content of approximately 10 parts per million and themass was boiled for 3 hours in a jacketed tank. The slurry wascentrifuged to a content of "about 1 part of water per part ofcellulose. While still in the rotating centrifuge, the wet cellulose matwas extracted by spraying onto it while the centrifuge was operatingsuccessive amounts of acetic acid of'increasing concentration, such aswas obtained by saving the effluent from previously dewatered batches.By so doing a counter current system is effected with a minimum use offinal glacial dewatering acid. The first obtained, most dilute acid wassent to recovery to oncentrate the same.

The acid wet cellulose was centrifugeddown so as to contain 1 part ofacid and 0.01'to 0.03 partof water per part of dry cellulose. Thiscellulose was then charged directly to an acetyl-a'to'r-containing 3parts'of acetic anhydride and .05 part of sulfuric acid catalyst and wasacety lated therein. The cellulose reacted rapidly-to of unacetylatedparticles therein. Example II 4 Q The procedure of the preceding examplewas repeated except that butyric acid was employed to remove the waterfrom the ccllulose'after'the boiling and removal of the bulk of thewater by centrifuging. The activated cellulose containing' b'u-tyricacid was charged into an este'rifica tion mixer containing 4 /2 parts ofbutyric anhydride and .04 part of sulfuric acid catalyst and thecellulose was butyrated, the temperature being controlled so that it didnot exceed 90 F. over the entire reaction. The cellulose reacted readilyto give amass of high clarity.

Example III :One :part of wood cellulose sulfite pulpuo'f highalpha-0611111086 content was slurried and boiled with parts ofdemineralized vwater having a mineral :content of approximately'lO:partszcp The following examples illustrate our invenmillion for 3 hoursin a jacketed tank. This slurry was then thinned with more water so thatthe pulp could be formed into a web on a perforated stainless steel beltsimilar to that used on the wet end of a paper machine. This celluloseweb on the perforated belt was then passed over suction boxes to removethe excess water and, following this, over a sequence of suction boxeswhere it was sprayed with acetic acid of increasing concentration in acounter current manner. From the last spray and suction box thecellulose mat through a picker or hammer mill and charged to anacylation mixer containing 4 parts of butyric anhydride and 0.05 partsulfuric acid catalyst. The cellulose reacted rapidly to a clear dope ofcellulose acetate butyrate free from any unreactedcellulose particles.

Example IV The cellulose boiling procedure of Example III was repeatedexcept cotton linters were used. Following this buty'r'icacid was usedas the water extractant instead of acetic acid in passing the celluloseweb over the counter current spray and suction box dewatering device.The cellulose mat delivered from the last suction box was damp with 2parts 'butyric acid. This pulp was then charged-without furthercentrifuging to an acylation mixer containing 4 ,4 parts 'butyricanhydride and'0.05 part sulfuric acid catalyst. The ensuing reaction toa cellulose tributyrate was somewhat slower than to the mixed estershown in Example III but the reaction was complete to an The samepulping and boiling procedure was used .as .in Example III. However, inorder to effect the countercurrent removal of water, an Oliver suctionfilter was used. This filter was equipped with a number of sprays sothat acetic acid :of increasing concentration could be passed throughthe cellulose mat in a countercurrent manner. After removal from theOliver filter, the mat was passed through squeeze rolls where the acidwas finally removed to 1 remaining part substantially free from water.This acetic acid damp cellulose was then charged to an acylation mixeras in Example III-and a high butyryl mixed ester was prepared b'yrapidly reacting to a dope free from unacylated cellulose particles,

Example VI Que part of high a-lpha sulfite pulp was slurried in 25 partsof :distilled water and the mass was boiled-for- 3.hours; The slurry wascentrifuged to removethe' bulk of the water and then dewateredbysprayingaceticacid onto the centrifuging pulpma'ssiun'til acellulosewas obtained having .1 :part of acid and substantiall no water (lessthan 0.02 part) per part of cellulose. The cellulose was picked apartand mixed with butyrlc anhydrideland ;-a little sulfuric acid catalystin .an acylation mixer cooled so that the temperature :never exceeded F.A cellulose ester of :good rquality was obtained.

When the term fisubstantially free of water is used herein it is to beunderstood toimean.

less than-0&5 part of Water .and preferably less than 0.03 part ispresent per part of dry cellulose.

We claim:

1. A method of activating cellulose containing a small amount ofhornified amorphous material which is particularly resistant toacylation which consists in boiling a suspension of the cellulose in alarge excess of water having a mineral content of less than 20 parts permillion for two to four hours, subjecting the cellulose mass to pressureto remove water, at least one part of water remaining per part ofcellulose and subsequently displacing the water in the cellulose with afatty acid of 2-4 carbon atoms so as to give a cellulose containingfatty acid but substantially free of water therein.

2. A method of activating cellulose containing a small amount ofhornified amorphous material which is particularly resistant toacylation which consists in boiling a suspension of the cellulose in alarge excess of distilled water for two to four hours, subjecting thecellulose mass to pressure to remove Water, at least one part of waterremaining per part of cellulose and subsequently displacing the water inthe cellulose with a fatty acid of 24 carbon atoms so as to give acellulose containing fatty acid but substantially free of water therein.

3. A method of activating cellulose containing a small amount ofhornified amorphous material which is particularly resistant toacylation which consists in boiling a suspension of the cellulose in alarge excess of Water having a mineral content of less than 20 parts permillion for two to four hours, subjecting the cellulose mass to pressureto remove water, at least one part of water remaining per part ofcellulose and subsequently displacing the water in the cellulose withacetic acid so as to give a cellulose containing acetic acid butsubstantially free of water.

4. A method of activating cellulose containing a small amount ofhornified amorphous material which is particularly resistant toacylaticn which consists in boiling a suspension of the cellulose in alarge excess of water having a mineral content of less than 20 parts permillion for two to four hours, subjecting the cellulose to pressure toremove water, at least one part of water remaining per part of celluloseand subsequently displacing the water in the cellulose by a concurrenttreatement thereof with acetic acid so as to give a cellulose containingacetic acid but substantially free of water therein.

5. A method of preparing cellulose acetate butyrate having a highbutyryl content from a cellulose containing a small amount of hornifiedamorphous material which is resistant to acylation which consists infirst boiling the cellulose in suspension in a large excess of lowmineral content water, subjectin the cellulose to pressure to removewater, at least one part of water remaining per part of cellulose,displacing the water in the cellulose with acetic acid and thenesterifying the cellulose with an esterification mixture comprisingbutyric anhydride and an acylation catalyst.

WILLIAM B. HINCKE. CARL J. MALM.

REFERENCES CITED The following referenlces are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,752,596 Hubert et a1 Apr. 1,1930 2,087,263 Olsen July 20, 1937 2,112,115 Richter Mar. 22, 19382,112,116 Richter Mar. 22, 1938 2,152,071 Malm Mar, 28, 1939

